Conventionally, a technique is available wherein, for example, duplexing (synthesis; Equivalent Copy) of data is carried out among a plurality of storage sections 101 to 104 in such a storage section controlling system 100 as illustrated in FIG. 8.
a host 105 for processing data stored in the storage sections (storage apparatus; disks) 101 to 104 as a processing target, a storage section controlling apparatus [given as “CM (Centralized Module)” in FIG. 8] 110 for carrying out processing for the storage sections 101 and 102 in accordance with an access request (reading/writing request) from the host 105, another storage section controlling apparatus (given as “CM” in FIG. 8) 120 for carrying out processing for the storage sections 103 and 104 in accordance with an access request from the host 105, channel adapters [given as “CA (Channel Adapter)” in FIG. 8] 113a and 113b for carrying out interface control between the host 105 and the storage section controlling apparatus 110, channel adapters (given as “CA” in FIG. 8) 123a and 123b for carrying out interface control between the host 105 and the storage section controlling apparatus 120, fibre channels [given as “FC (Fibre Channel)” in FIG. 8] 114a and 114b for carrying out interface control between the storage section controlling apparatus 110 and the storage sections 101 and 102, and fibre channels (given as “FC” in FIG. 8) 124a and 124b for carrying out interface control between the storage section controlling apparatus 120 and the storage sections 103 and 104.
It is to be noted that the storage section controlling apparatus 110 and 120 include CPUs (Central Processing Units) 111 and 121 for executing data processing, and caches 112 and 122, respectively. Further, a storage apparatus 106 is configured from the storage section controlling apparatus 110 and 120, CAs 113a, 113b, 123a and 123b, FCs 114a, 114b, 124a and 124b and storage sections 101 to 104.
Then, in the storage section controlling system 100, the storage section controlling apparatus 110 and 120 cooperate with each other to copy data in a predetermined region of the storage section 102 into the storage section 103 to duplex the data in the predetermined region.
In particular, the storage section controlling apparatus 110 and 120 execute data copy in the predetermined region of the storage section 102 and copy the data of the storage section 102 which is a copying source into the storage section 103 which is a copying destination to maintain the data in the predetermined region in a duplexed state.
Therefore, the storage section controlling system 100 is configured such that, while the storage section 102 and the storage section controlling apparatus 110 function as a master side, the storage section 103 and the storage section controlling apparatus 120 function as a slave side. Further, while the host 105 transmits a reading (readout) request of data to both of the storage section controlling apparatus 110 and 120 such that the storage sections 102 and 103 are taken as targets, a writing request is transmitted only to the storage section controlling apparatus 110 such that the storage section 102 is taken as a target.
In the storage section controlling system 100, within a period after data copying is started until copying of data of all target regions is completed to enter a duplexed state at an initial stage for implementing duplexing, readout of data from a data storage region (volume) of the storage section 103 as a copying destination is inhibited because the data is not guaranteed.
For example, even if a readout request for a duplexing target region of the storage section 102 is issued from the host 105 before duplexing is completed, there is no guarantee that duplexed data can be read out. Therefore, the storage section controlling apparatus 120 is configured such that it sends back an error response to the host 105 or takes some other countermeasure to suppress a data readout process for the storage section 103 from the storage section controlling apparatus 120.
Accordingly, the user or the like of the host 105 cannot read out data from the storage section 103 which is a copying destination before duplexing is completed, and this is inconvenient.
It is to be noted that a technique (remote copying) is conventionally available wherein duplication of data in a storage region which is a duplication source is managed also in another storage region which is a duplication destination upon restoration of a storage system from a disaster, and another technique is available wherein, if a readout request is issued to a duplication destination in which duplication is not completed as yet during such remote duplication, then data corresponding to the readout request is requested to a duplication source and the readout request is dealt with after the data is received (for example, refer to Patent Document 1).    Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-165618
In the conventional storage section controlling system 100 described above with reference to FIG. 8, it is preferable to execute a readout request for data duplicated in the storage section 103 which is a copying destination based on the latest data of the storage section 102 which is a copying source commonly before and after completion of duplexing.
For example, when a readout request for the storage section 103 is issued, if an updating process of corresponding data (source data) of the storage section 102 corresponding to the readout request is being carried out, then it is preferable to read out the data after updated.
In the storage section controlling system 100, a processing order of reading/writing requests from the host 105 at least for the storage sections 102 and 103 which are duplexing targets of data is managed with a queuing table (not illustrated). Accordingly, if an updating process of the source data is registered already in the queuing table, then it is desirable to use the data after the updating process for a response to the readout request for the storage section 103.
However, in the conventional storage section controlling system 100, even if an updating process (writing process) for source data during execution (during queuing) exists, data after the updating process cannot be used for a response to a readout request for a copying destination.